The invention relates to a method for visualizing a mark or signature mark on a spectacle lens, in which, in order to identify the signature mark, an illumination light beam is directed onto the spectacle lens, which impinges on the spectacle lens, after impinging on the spectacle lens is reflected at a reflector embodied as a retroreflector, impinges once again on the spectacle lens, and finally is passed as an observation light beam to a camera.
The invention furthermore relates to an apparatus for visualizing a mark or signature mark on a spectacle lens, comprising an illumination light source arranged on a first side of the spectacle lens and sewing for generating an illumination light beam, for identifying the signature mark, a reflector embodied as a retroreflector and arranged on that side of the spectacle lens which is situated opposite the first side, and a camera for receiving an observation light beam coming from the spectacle lens.
Spectacle lenses, in particular so-called, progressive lenses, are provided with marks or signature marks, the position of which is detected and processed during the production of the spectacle lens in order that the spectacle lens is clamped, processed and stamped in a correct position and is finally introduced into the end customer's spectacles. Signature marks are applied to spectacle lenses in a targeted manner and permanently, to be precise by means of diamond scribing methods, by means of impression during the moulding of plastic spectacle lenses or by means of laser signing. In addition, the term “signature marks” in the context of the present invention also encompasses other irregularities—not applied in a targeted manner—of the spectacle lens, e.g. streaks or striations in the glass material or plastic.
When “spectacle lenses” are mentioned in the context of the present application, they should also be understood to mean contact lenses and other comparable optical components.
In order that the person wearing the spectacles is not disturbed by signature marks applied in a targeted manner during the use of the spectacles, said marks are designed such that they are discernible only under very specific lighting conditions. Therefore, it is difficult to identify the position of a signature mark on a spectacle lens during the production process. An additional complicating factor here is that the spectacle lenses in the production process have very different optical powers on account of the specific requirements of the persons subsequently wearing the spectacles. Within production, therefore, spectacle lenses having these different optical powers closely succeed one another, which therefore have to be taken into consideration in quick succession during the successive processing of individual spectacle lenses.
For monitoring progressive lenses at the distant and near reference points it is necessary to measure the power of the progressive lenses at defined coordinates on the spectacle lens, depending on the applied signature marks. The signature marks therefore have to be visualized for a manual or an automatic measurement. In the case of known methods and apparatuses, this is done by means of rhomboidal gratings or striped patterns which are imaged unsharply and the bright/dark edge transitions of which make the signature mark discernible.
What is disadvantageous about this known procedure, in particular during automatic identification of the signature marks, is that the grating is imaged with different magnifications depending on the power of the spectacle lens examined, namely depending on the respective dioptric power of the spectacle lens. It is therefore necessary, for identifying the signature marks, to implement a considerable complexity with regard to the algorithms used. Known methods hitherto have not led to totally reliable automatic identification. It is therefore necessary in practice nowadays that even in the case of automated test installations, specially trained workers have to intervene manually in the production process and correct erroneous identifications.
However, even when the signature marks are identified by means of a manual test procedure within a production process, the situation is similar. In this case, depending on the signature method used, different illumination is used to visualize the signature marks. In the case of known apparatuses, this is done by rearranging or changing over illumination units or the spectacle lens is led past under suitable illumination conditions, e.g. a remote bright-dark edge, and is observed. However, even with these methods the marks themselves can only be discerned unclearly, with the result that errors are possible in the positioning and orientation of the respective spectacle lens. This holds true also and precisely with regard to the time available for identifying the signature mark. For these reasons, particularly in the conventional procedure for preparing spectacle lenses it is necessary to mark out (“to dot”) the spectacle lenses at the location of the signature mark by means of a felt tip pen or the like, which requires additional outlay in terms of labour and time.
Corresponding considerations also hold true for another area within the processing of such spectacle lenses, namely for automatic stamping machines, which, according to the present-day prior art, likewise need the assistance of an operator. Said operator observes the spectacle lenses on a screen in order to correct positions of signature marks that have not been automatically identified manually in the system, for example by means of trackball input. This disadvantage is likewise manifested in a reduction of the productivity of the video-assisted, manually actuated stamping machines.
U.S. Pat. No. 3,892,494 suggests a method and an apparatus for finding optical microeffects on optical components, for example lenses. In this case, a laser beam is directed through a beam splitter, namely a partly transmissive mirror, onto the component to be examined. The laser beam passes through the component and impinges, on the opposite side, on a retroreflector, for example a retroreflective film, from which it is reflected again through the component and returns along the same beam path until it is deflected at the beam splitter and directed onto a camera.
What is disadvantageous about this known procedure is that it can lead to problems in the case of spectacle lenses having very different flexures. This is because, owing to the very different flexures, the observation beam path has to be long and additionally stopped down in order to obtain a sufficient depth of focus. On the other hand, however, the structures of the retroreflector should not be imaged sharply, since it is indeed desirable to have a relatively homogeneous background in order to avoid misinterpretations. Consequently, in these applications the retroreflector has to he situated very far behind the plane of the spectacle lens to be measured and, in addition, it would have to be very large because strongly negative spectacle lenses image the retroreflector in a greatly demagnified fashion, such that the whole lens can no longer be seen over the retroreflector.
An additional factor is that in the context of the present invention it is not just a matter of identifying signature marks and other irregularities on spectacle lenses, but rather integrating this identification process into a measuring apparatus or into a processing process. In that case, however, a sensor is arranged behind the spectacle lens, that is to say on the same side as the retroreflector in the known apparatus, in order to measure physical properties of the spectacle lens. Therefore, for structural reasons it is not possible to arrange the retroreflector very far behind the plane of the spectacle lens in this case.
U.S. Pat. No. 4,310,242 suggests an arrangement for measuring the optical quality of windscreens on site. This also involves using an optical arrangement comprising a light source, a beam splitter, a retroreflector positioned behind the windscreen to be measured, and a camera. In this case, a fine pattern is projected through the beam splitter onto a retroreflective screen, in such a way that a real image of said pattern, which is deformed by the windscreen situated in the beam path, arises on the retroreflective screen. Via the beam splitter, the camera then likewise looks at the retroreflective screen in the protection direction through the windscreen to be tested. Inhomogeneities, stress birefringences, striations, etc. become clearly visible in this way,
DE 43 43 345 A1 suggests methods and apparatuses for measuring the reflective and/or transmissive optical properties of a sample. In this case, measurement radiation is directed on to a sample and is reflected by the sample, such that it passes to a retroreflector, which sends the measurement radiation back again via the object to the light source, where coupling-out to a detector takes place. A further similar procedure is also described in EP 0 169 444 A2.
In a known vertex refractometer “Focovision SPV 1”, a light beam is sent from a light source through a green filter and directed via a beam splitter on to the spectacle lens to be tested. The light beam passes through the spectacle lens and passes to a sensor head arranged behind the rear side of the spectacle lens. Physical properties of the spectacle lens can be measured in this way. Furthermore, a plane in which exchangeable illumination ancillary units can be arranged is situated on the rear side. These illumination ancillary units illuminate the spectacle lens from the rear, such that the signature marks become visible. A corresponding observation light beam passes from the spectacle lens to the beam splitter, is reflected there and is then led via further optical means to a camera. In the case of a first illumination ancillary unit, a very sharply delimited bright beam of light is directed onto the spectacle lens at a shallow angle. Signature marks that were produced by scratching then become brightly luminous against a dark background on account of the irregular shape of the scratch mark. By contrast, the second illumination ancillary unit is provided for spectacle lenses whose signature marks were not produced by scratching, but rather by impression or by laser beams. Said second illumination ancillary unit has a bright line grating illuminated from below and a plurality of auxiliary lenses which are arranged alongside one another and with which these luminous gratings are imaged to infinity.
The known apparatus is therefore relatively complex in terms of operating control. Furthermore, the location at which the measurement beam emitted by the light source is incident on the spectacle lens coincides with the location, at which the observation light beam emerges from the spectacle lens. This can lead to disturbances during the evaluation.
U.S. Pat. No. 5,867,259 also suggests an observation apparatus for concealed markings, i.e. signatures. In the case of this apparatus, a lens provided with the concealed marking is illuminated with an illumination light. The concealed marking is then observed as a shadow of the lens formed by the illumination light.
This apparatus has the disadvantage that the marking, depending on the type of lens, is displaced by the local prismatic effect thereof or is demagnified or magnified by the converging or diverging effect of the lens.
Furthermore, the documents U.S. Pat. Nos. 7,728,962 and 7,423,741 suggest an apparatus for visualizing a signature mark on a spectacle lens. Said documents propose moving, e.g. rotating, the retroreflector in order to obtain a background that is as homogeneous as possible and to blur the structures of the retroreflector.
In the case of such a simply rotating retroreflector, its angular velocity near the axis of rotation is very low, with the result that only little blurring of its structures occurs here. Therefore, the retroreflector should perform as far as possible a movement in the manner of a parallel rotary translation, e.g. on a cycloidal path. However, such movements, particularly if they are to be performed with a high frequency, can be balanced only with difficulty, and so the outlay in terms of apparatus is very high.
Therefore, the invention, is based on the problem of developing methods and apparatuses of the type mentioned in the introduction to the effect that the disadvantages mentioned are avoided. In particular, the intention is to make it possible to treat spectacle lenses within a production process in such a way that the signature marks applied thereto are identified in the correct position. All this is to be done with the simplest possible means appertaining to apparatus and method.